In The Deathly Hallows, Aberforth Dumbledoe told Harry, Ron, and Hermione about everything that happened between his brother Albus and Grindelwald as teenagers. When Aberforth confronted the two conspiring friends about taking the ill young Ariana with them on their quest for Muggle domination, an “argument” turned into a fight and Grindelwald hit Aberforth with the Cruciatus Curse. Albus defended his brother, and the three boys dueled; the fight resulted in a stray curse hitting Ariana, killing her instantly. Grindelwald fled, and neither Aberforth and Albus knew which of the three had cast the fatal blow. Albus was so haunted by the possibility it had been him that he put off fighting the Dark Wizard for decades for fear of learning the truth. Or so he said.

The Crimes of Grindelwald taught us that Dumbledore couldn’t have faced Grindelwald even if he wanted to, because the two had agreed to a blood pact never to fight one another. But if they had already made that apparently unbreakable promise, how did Dumbledore fight Grindelwald the night his sister died?

A blood pact is an entirely new concept in J.K. Rowling’s wizarding world, so we don’t know much about how it works. It’s not equivalent to an Unbreakable Vow, which kills you if you don’t uphold it; if it were, both Dumbledore and Grindelwald would have died that night in Godric’s Hollow when they dueled. A blood pact must also be possible to destroy since Dumbledore will eventually fight Grindelwald in 1945 in the most famous duel ever. But a blood pact is still strong enough that Dumbledore couldn’t violate its magical agreement until he found a way to undo it, which he wasn’t even sure he could do at the end of The Crimes of Grindelwald.

So what happens to a wizard who does violate a blood pact? What if a wizard fights someone they made a magical pact not to? Does the blood pact protect them like a shield charm? Do the curses vanish, or get absorbed by the protective guard? Or do the curses simply bounce off of them? Or does something much more dangerous, and therefore something much more reckless, happen: do they ricochet, potentially hitting innocents nearby? Is this what happened to Ariana Dumbledore?

After hearing Aberforth’s story, Harry understood that while going mad as a result of Voldemort’s cursed potion in The Half Blood Prince, Dumbledore had relived the night his sister died. Until now, Dumbledore’s pitiful cries didn’t totally fit with the story of that fatal night. It always seemed like Dumbledore jumped to his brother’s aid after the argument turned violent, but Dumbledore’s rantings included him begging Grindelwald not to hurt them. It was as though Albus knew he couldn’t fight Grindelwald. From The Half Blood Prince:

“It’s all my fault, all my fault,” he sobbed. “Please make it stop, I know I did wrong, oh please make it stop and I’ll never, never again…”

Dumbledore drank like a child dying of thirst, but when he had finished, he yelled again as though his insides were on fire. “No more, please, no more…”

…Dumbledore began to scream in more anguish than ever. “I want to die. I want to die! Make it stop, make it stop, I want to die!”

“KILL ME!”

It’s not clear which of those cries were Dumbledore’s memories and which were the screams of a man being poisoned, but it does seem like Dumbledore pleaded with Grindelwald not to hurt his brother and sister before the duel. What exactly happened that night in Godric’s Hollow is more of a mystery than ever. We might never know the entire story of what happened when the Dumbledore brothers dueled with Grindelwald, but it does seem like that fateful blood pact haunted Dumbledore his entire life because it led to his sister Ariana’s death.

What do you think happened that night? Did the blood pact lead to Ariana being killed? Giev us your best theory in the comments below.